Enhanced fitness of SARS-CoV-2 variant of concern Alpha but not Beta.

Emerging variants of concern (VOCs) are driving the COVID-19 pandemic1,2. Experimental assessments of replication and transmission of major VOCs and progenitors are needed to understand the mechanisms of replication and transmission of VOCs3. Here we show that the spike protein (S) from Alpha (also known as B.1.1.7) and Beta (B.1.351) VOCs had a greater affinity towards the human angiotensin-converting enzyme 2 (ACE2) receptor than that of the progenitor variant S(D614G) in vitro. Progenitor variant virus expressing S(D614G) (wt-S614G) and the Alpha variant showed similar replication kinetics in human nasal airway epithelial cultures, whereas the Beta variant was outcompeted by both. In vivo, competition experiments showed a clear fitness advantage of Alpha over wt-S614G in ferrets and two mouse models-the substitutions in S were major drivers of the fitness advantage. In hamsters, which support high viral replication levels, Alpha and wt-S614G showed similar fitness. By contrast, Beta was outcompeted by Alpha and wt-S614G in hamsters and in mice expressing human ACE2. Our study highlights the importance of using multiple models to characterize fitness of VOCs and demonstrates that Alpha is adapted for replication in the upper respiratory tract and shows enhanced transmission in vivo in restrictive models, whereas Beta does not overcome Alpha or wt-S614G in naive animals.

Inactivation of SARS-CoV-2 on salt-coated surfaces: an in vitro study.

In the COVID-19 pandemic, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), face masks have become a very important safety measure against the main route of transmission of the virus: droplets and aerosols. Concerns that masks contaminated with SARS-CoV-2 infectious particles could be a risk for self-contamination have emerged early in the pandemic as well as solutions to mitigate this risk. The coating of masks with sodium chloride, an antiviral and non-hazardous to health chemical, could be an option for reusable masks. To assess the antiviral properties of salt coatings deposited onto common fabrics by spraying and dipping, the present study established an in vitro bioassay using three-dimensional airway epithelial cell cultures and SARS-CoV-2 virus. Virus particles were given directly on salt-coated material, collected, and added to the cell cultures. Infectious virus particles were measured by plaque forming unit assay and in parallel viral genome copies were quantified over time. Relative to noncoated material, the sodium chloride coating significantly reduced virus replication, confirming the effectiveness of the method to prevent fomite contamination with SARS-CoV-2. In addition, the lung epithelia bioassay proved to be suitable for future evaluation of novel antiviral coatings.

Development of a set of simple bacterial biosensors for quantitative and rapid measurements of arsenite and arsenate in potable water.

Testing for arsenic pollution is commonly performed with chemical test kits of unsatisfying accuracy. Bacterial biosensors are an interesting alternative as they are easily produced, simple, and highly accurate devices. Here, we describe the development of a set of bacterial biosensors based on a nonpathogenic laboratory strain of Escherichia coli, the natural resistance mechanism of E. coli against arsenite and arsenate, and three reporter proteins: bacterial luciferase, beta-galactosidase and Green Fluorescent Protein (GFP). The biosensors were genetically optimized to reduce background expression in the absence of arsenic. In calibration experiments with the biosensors and arsenite-amended potable water, arsenite concentrations at 4 microg of As/L (0.05 microM) were routinely and accurately measured. The currently most quantitative system expressed the bacterial luciferase as reporter protein, responding proportional with a concentration range between 8 and 80 microg of As/L. Sensor cells could be stored as frozen batches, resuspended in plain media, and exposed to the aqueous test sample, and light emission was measured after 30-min incubation. Field testing for arsenite was achieved with a system that contained beta-galactosidase, producing a visible blue color at arsenite concentrations above 8 microg/L. For this sensor, a protocol was developed in which the sensor cells were dried on a paper strip and placed in the aqueous test solution for 30 min after which time color development was allowed to take place. The GFP sensor showed good potential for continuous rather than end point measurements. In all cases, growth of the biosensors and production of the strip test was achieved by very simple means with common growth media, and quality control of the sensors was performed by isolating the respective plasmids with the genetic constructs according to simple standard genetic technologies. Therefore, the biosensor cells and protocols may offer a realistic alternative for measuring arsenic contamination in potable water.